带限局部平面波传播算子与偏移方法

Band-limited local plane wave propagator and migration

地震信号的带限特点限制了高频近似下的射线类算子在地震波模拟和偏移中的应用。本文基于射线理论构建带限信号局部平面波传播算子,兼顾射线类方法具有时空局部性和实现灵活高效的特点,有效进行带限地震波场的模拟和偏移。即分析传统高频射线在速度界面的传播特征,利用带限信号频带与菲涅耳带的关系,构建带限斯奈尔定律进行中心射线传播;在局部平面波假设下,基于带限中心射线做旁轴近似展开,构建带限局部平面波传播算子;在此基础上发展基于该算子的带限射线束偏移方法。数值实验结果表明,带限射线束较传统基于高频近似的射线束具有更强穿透能力,改善射线阴影区照明,从而提高复杂构造区成像质量。

The seismic signal is a kind of band-limited signal,and it limits the application of ray-based operators to seismic wave propagation and migration under the infinite high-frequency approximation.With the framework of conventional ray theory,this paper proposes a band-limited local plane wave propagator.Characterized by local space linearity and implementation flexibility,the propagator can effectively perform band-limited seismic wavefield propagation and migration.Based on the propagation characteristics of high-frequency rays between intervals,the band-limited Snells law is obtained for the central ray propagation with the relationship between the first Fresnel zone and the frequency band of signals.Then,the band-limited local plane wave propagator can be built with paraxial approximation under the local plane wave as-sumption.Finally a band-limited beam migration method is developed.Numerical experiments demonstrate that the band-limited beams have better illumination in ray-shadow areas and are beneficial to improve the imaging resolution in complex structures.